Two young boys encounter a fugitive and form a pact to help him evade the vigilantes that are on his trail and to reunite him with his true love.

Two boys, Ellis and his friend Neckbone, find a man named Mud (McConaughey) hiding out on a deserted island in the Mississippi River. Mud tells the boys fantastic stories, including how he had to kill a man to save his true love Juniper (Witherspoon), and that the man's family has been chasing him ever since.

Skeptical but intrigued, Ellis and Neckbone agree to help reunite Mud with Juniper, and soon Mud's tall tales come to life when their small town is besieged by bounty hunters out for blood.